This invention generally relates to motor vehicle air bags. More particularly, the invention relates to a driver side air bag module having an integral horn switch, which is easily and reliably actuated.
A driver side air bag module is typically mounted upon a motor vehicle""s steering wheel. A typical module includes a mounting plate or housing attached to the hub of the steering wheel, an inflator mounted to the mounting plate, an air bag and a cover. The prior art teaches that horn switches can be placed within spokes of the steering wheel. The placement of this type of horn switch can be bothersome because it is difficult to install in the steering wheel, is not aesthetically pleasing, and it is often difficult for the driver of the vehicle to find and activate the horn. Several other designs have incorporated various horn mechanisms into the air bag module. One class of vehicle modules is floated on a spring assembly within a steering wheel assembly relative to a fixed, externally mounted horn switch, also mounted on the steering wheel. An electrical contact of the horn switch is placed on both the module and the wheel. To actuate the horn, the entire module is moved toward the steering wheel hub, closing the contacts and activating the horn. This method of horn switch design is expensive and requires a large gap between the module and the steering wheel so the module can float.
Another problem with floating horns/modules is that they are susceptible to vibration because the weight of the module must be supported by the springs. As a result, large springs must be used to avoid inadvertent actuation during vibration, jolt, bounce, etc., which in turn leads to high forces and displacements to activate the horn.
Another type of horn switch mounts a thin, flexible membrane switch on the back or inner surface of the air bag module cover. Membrane switches conventionally comprise two very thin non-conductive sheets having conductive coatings separated by thin spacers. Pressure on the switch moves the conductive surfaces together to close an electrical circuit and actuate the horn. The membrane switches are expensive and their installation is labor intensive. In the case of a malfunction of the horn switch, the entire cover must be replaced, as the membrane switch is an integral part of the cover.
Membrane horns have adequate appearance and actuation properties, but they also have problems with inadvertent horn actuation. This is typically caused when the air bag cushion is not folded properly (or expands over time), placing undo pressure on the membrane. In other instances, extreme hot or cold temperatures can cause the cover to expand or contract, which activates the member switch causing the horn to actuate.
Automotive horns contained in air bag modules have also proven extremely difficult to manufacture because of the stringent requirements placed on them. These include specific requirements on the force and displacement used to activate the horn, appearance, and resistance to inadvertent activation due to vibration.
It is the object of the present invention to eliminate these concerns. In the preferred embodiment, the horn switch consists of six components: a lower housing, upper housing, lower contact, upper contact, an optional wave spring, a wiring harness, and an adhesive disk. Activation of the horn occurs when the upper contact touches the lower contact, completing an electrical circuit.
It is a further object of the invention to provide an air bag module with a reliable horn switch, which allows for a module of reduced size. Other objects, features, and advantages will become apparent from the following description and appended claims.
Accordingly the invention has a driver side air bag module having an air bag cover, mounting plate, retaining ring, inflator, and cushion. The driver side air bag module cover includes a relatively flexible horn actuation area, which is depressible from its front surface by a driver. A horn switch assembly is provided inside the air bag module. The horn switch assembly is disposed on the inflator and is mounted behind the horn actuation area. This horn switch is electrically coupled to the horn by means of a wire harness, which passes through the inner diameter of the retaining ring and through the mounting plate. When the flexible horn actuation area is depressed, the horn switch couples the contacts and the electrical connection is made, which activates a horn.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for the purpose of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.